1. Field of the Invention
The present invention relates to a method for manufacturing a display substrate, and more particularly to a method for manufacturing a display substrate in which opposite substrates can be easily assembled by accurate alignment.
2. Description of Related Art
A display panel of a liquid crystal display device (LCD) contains a color filter substrate, a thin film transistor (TFT) array substrate, and a liquid layer interposed therebetween.
In a process of assembling a liquid crystal panel, a gap is formed between the two substrates owing to existence of spacers while assembling the substrates. In this process, a highly accurate alignment technique for assembling the two substrates is required, or else light leakage of the panel due to misalignment occurs thereby impairing panel brightness.
Multi-domain vertical alignment (MVA) technique features prompt signal response time, wider viewing angles, efficient improvement in mura issues, promotion of transmittance and contrast ratio, and perfection of display quality. In the MVA technique of manufacturing upper and lower substrates, bumps and slits are arranged alternately so that liquid crystal molecules tilt in a certain angle while no electric field is applied. If an electric field is applied, the tilt angle of the liquid crystal molecules changes rapidly so that backlight can pass through the liquid crystal faster, which results in a significant decrease of display time. Besides, the liquid crystal molecules align in the certain angle because of the bumps so as to extend the viewing angle.
In the process for assembling panels of conventional MVA-LCDs, a black matrix and a metal electrode layer (a gate or drain) respectively on a color filter and a TFT substrate serve as alignment marks. In the process manufacturing the color filter substrate, the black matrix and bumps are aligned in accuracy of ±3 μm, and accuracy of assembling panels is below ±5 μm. Therefore, alignment accuracy between the bumps on the color filter substrate and the slits on the TFT substrate is of error about ±8√{square root over ( )}2 μm which causes domain abnormality which affects brightness of the panel.
A method for manufacturing a color filter substrate is disclosed in US patent publication No. 2005/0106477A1. A structure of the color filter substrate is shown in FIG. 1. While manufacturing color filter layers 303a, 303b, and 303c, an alignment mark area on a non-active area of a substrate 301 is enclosed by hydrophobic color material serving as barriers 311, 312. At the same time of manufacturing a black matrix 302, the black matrix material is also injected between the barriers 311 and 312 so as to form an alignment mark 310 which benefits alignment accuracy between the two substrates during assembly.
However, the technique disclosed in the prior art described above only can be applied in methods for manufacturing color filter substrates requiring a black matrix because the alignment mark 310 and the black matrix 302 are made of the same material and formed at the same step. Besides, the foregoing technique can only be applied to alignment of assembling panel of TN-LCDs, i.e. alignment of the black matrix and the TFT substrate. Nevertheless, while assembling panels of MVA-LCDs, there is a requirement for alignment between the bumps and the slits respectively on the upper and lower substrates. Hence, the technique disclosed in US patent publication No. 2005/0106477A1 fails to satisfy a need for accurate alignment when that technique is applied in assembling panels of MVA-LCDs.
In order to overcome aforementioned difficulty, the industry makes efforts in development of methods for assembling panels of MVA-LCDs.